White-spotted bush frogs on daddy duty

New research by NUS Biological Sciences PhD candidate K. S. Seshadri has demonstrated the paternal devotion of critically endangered male white-spotted bush frogs in protecting their eggs from predators. This characteristic enhances the survival of their offspring, while confirming their role as sole caregivers.

Once presumed extinct, Mr Seshadri rediscovered the Raochestes chalazodes, or white-spotted bull frogs, in 2011 in the Western Ghats of India.

When there were no father frogs guarding the eggs, less than 30 per cent of the eggs in a clutch survived.

— Mr K. S. Seshadri, NUS Biological Sciences

Unlike other frog species who typically lay their eggs in or above standing water, the white-spotted bush frogs lay their eggs within the hollow internodes of reed bamboo that grow along streambanks. The males, which typically measure about 2cm in length, squeeze into the narrow openings — often less than 10mm long and 4mm wide — of the reed bamboo internodes. Once they have found a suitable spot for spawning, ideally one with holes at the base so that rainwater does not collect and drown the eggs, they call out for female mates who respond by entering the bamboo and laying their eggs on the inner walls. The female leaves once the male frog has fertilised the eggs.

Endoscopes were used to observe more than 40 clutches of eggs daily across two breeding seasons in 2015 and 2016. Findings showed that the father frogs guarded their eggs by sitting on them, possibly to keep the eggs hydrated, for up to 47 days until all the eggs had either hatched or perished, leaving only once each evening to hunt for prey nearby. They also lunged at intruders and made incessant alarm calls to ward off cannibalistic rivals wanting to feed on the eggs for nutrition or to invade territory and reduce competition for resources.

“Predation by other male frogs is the main cause of egg mortality of white-spotted bush frogs. When there were no father frogs guarding the eggs, less than 30 per cent of the eggs in a clutch survived,” said Mr Seshadri.

The findings of the study, done in collaboration with the University of La Verne, were published in the scientific journal Behavioural Ecology and Sociobiology on 14 December 2017.